1. Field of the Invention
The subject invention relates to test and debug of semiconductor chips using device photoemission.
2. Related Art
It has been well known in the art that semiconductor devices emit light upon change of states, e.g. transistors switching on/off. This phenomenon has been used successfully to test and debug semiconductor circuits using, e.g., infrared emission microscopy (IREM) and time-resolved emission microscopy. It has also been known in the art to use lasers to test and debug semiconductor circuits by examining modulations in the reflected laser light. The technique is generally referred to as LP (laser probing). For more information the reader is directed to review U.S. Pat. Nos. 5,208,648, 5,220,403 and 5,940,545, which are incorporated herein by reference in their entirety. Additional related information can be found in Yee, W. M., et al. Laser Voltage Probe (LVP). A Novel Optical Probing Technology for Flip-Chip Packaged Microprocessors, in International Symposium for Testing and Failure Analysis (ISTFA), 2000, p 3-8; Bruce, M. et al. Waveform Acquisition from the Backside of Silicon Using Electro-Optic Probing, in International Symposium for Testing and Failure Analysis (ISTFA), 1999, p 19-25; Kolachina, S. et al. Optical Waveform Probing—Strategies for Non-Flip-chip Devices and Other Applications, in International Symposium for Testing and Failure Analysis (ISTFA), 2001, p 51-57; Soref, R. A. and B. R. Bennett, Electrooptical Effects in Silicon. IEEE Journal of Quantum Electronics, 1987. QE-23(1): p. 123-9; Kasapi, S., et al., Laser Beam Backside Probing of CMOS Integrated Circuits. Microelectronics Reliability, 1999. 39: p. 957; Wilsher, K., et al. Integrated Circuit Waveform Probing Using Optical Phase Shift Detection, in International Symposium for Testing and Failure Analysis (ISTFA), 2000, p. 479-85; Heinrich, H. K., Picosecond Noninvasive Optical Detection of Internal Electrical Signals in Flip-Chip-Mounted Silicon Integrated Circuits. IBM Journal of Research and Development, 1990. 34(2/3): p. 162-72; Heinrich, H. K., D. M. Bloom, and B. R. Hemenway, Noninvasive sheet charge density probe for integrated silicon devices. Applied Physics Letters, 1986. 48(16): p. 1066-1068; Heinrich, H. K., D. M. Bloom, and B. R. Hemenway, Erratum to Noninvasive sheet charge density probe for integrated silicon devices. Applied Physics Letters, 1986. 48(26): p. 1811; Heinrich, H. K., et al., Measurement of real-time digital signals in a silicon bipolar junction transistor using a noninvasive optical probe. IEEE Electron Device Letters, 1986. 22(12): p. 650-652; Hemenway, B. R., et al., Optical detection of charge modulation in silicon integrated circuits using a multimode laser-diode probe. IEEE Electron Device Letters, 1987. 8(8): p. 344-346; A. Black, C. Courville, G. Schultheis, H. Heinrich, Optical Sampling of GHz Charge Density Modulation in Silicon Bipolar Junction Transistors Electronics Letters, 1987, Vol. 23, No. 15, p. 783-784, all of which are incorporated herein by reference in their entirety.
Recently a new phenomenon has been discovered that can also be utilized in test and debug of semiconductor devices. With the shrinking of the size of new devices, the devices are made “leaky” so that electron-hole recombination occurs during the static off state of the device, leading to photon (−IR) emission. This emission increases as design rule decreases. That is, this phenomenon will express itself more pronouncedly as device generation progresses. This static emission may also be used for debug and test of semiconductor circuits. For example, it has been suggested to use digital imaging software to overlay IREM images of static emissions over the die layout to investigate which elements emit photons. It was suggested to also overlay the state of each device over the IREM image to determine whether the emission means a “1” or “0” logical state. This manual methodology was used to investigate defects by imaging a device in two different logical states and observing whether the emission state has changed. For more information on this phenomenon and the image overlay methodology, the reader is directed to Infrared Emission-based Static Logic State Imaging on Advanced Silicon Technologies, Daniel R. Bockelman, Steve Chen, and Borna Obradovic; Proceedings from the 28th International Symposium for Testing and Failure Analysis, 3-7 Nov. 2002, Phoenix, Ariz., which is incorporated herein by reference in its entirety.
As can be understood from the above description and cited publication, while the image overlay technique may help investigate a failure, it is slow, tedious, and becomes more difficult as device generation advance and devices become smaller and denser. That is, the image overlay methodology requires the ability to obtain an image of sufficient resolution so that the various devices and emissions may be distinguished from each other and from surrounding noise. Moreover, photon emission from devices is a statistical phenomenon, so comparison of images using image editing software may provide erroneous conclusion unless the image is obtained over a statistically sufficiently long exposure duration or by performing the comparison over sufficiently large number of IREM images.
As devices get smaller and closely packed with newer generations, beneficial use of the emission detection techniques can only be made if the location of the emission can be isolated and accurately linked to the devices that actually emit the light. Similar issue applies to laser-based systems, i.e., to use such tester one must resolve which device caused the modulation in the reflected laser light. However, as design rule shrinks, the density of the devices increases, making it very difficult and sometimes impossible to isolate the device that emits the light or modulates the laser beam. Additionally, emissions from neighboring devices enter the optical path of the testing system, thereby further complicating the task of isolating the emitting or modulating device. Ironically, while design rule shrinking leads to improved static emission, it also makes it more difficult to isolate the emitting devices.
In order to enable progress in the semiconductor industry pursuant to “Moore's Law,” designers will continue to decrease design rules and increase device density. Therefore, the need for debug and testing becomes increasingly indispensable and the difficulty of resolving emitting/modulating devices must be solved.